However, it is still vitally important that you understand how your tools work. This is particularly critical when it comes to things like preprocessors, libraries and frameworks which aim to save you time by automating common processes and functions. For the most part, anything that saves you time is a Good Thing™ but it cannot be stressed enough that using tools like these in earnest should be avoided until you understand exactly what they are doing for you (and, to an extent, how they are doing it).
I would add Rails view helpers to this list.
Ultimately, you are responsible for anything that writes code on your behalf. The great thing is, though, on an open source stack, you can dig in and not only figure out how a tool works, but how well it works.
Inexperience can play out in two extremes: cobbling together other people's code, and rejecting anyone else's code with a not invented here mentality.